Null-balance indication system and variable transformer therefor



Jan. 16, 1962 Filed Sept. 15, 1958 K. G. HELLER ET AL NULL-BALANCE INDICATION SYSTEM AND VARIABLE TRANSFORMER THEREFOR 2 Sheets-Sheet 1 Jan. 16, 1962 K. G. HELLER ET A1. 3,017,588

NULL-BALANCE INDICATION SYSTEM AND VARIABLE TRANSFORMER THEREFOR Filed Sept. l5, 1958 2 Sheets-Sheet 2 www @Lam wrom/ifi United States Patent Oi 3,017,588 NULL-BALANCE INDICATION SYSTEM AND VARIABLE TRANSFORMER THEREEOR Kenneth GVHeller, Redwood City, and William Snyder,

Palo Alto, Calif., assignors to American Radiator &

Standard Sanitary Corporation, New York, N.Y., a

corporation of Delaware Filed Sept. 15, 1958, Ser. No. 761,019 1 Claim. (Cl. 336-135) `This invention relates to and in general has for its Object the provision of a null-balance indication system and a novel variable transformer therefor.

More specifically, one of the objects of this invention is the provision of a variable transformer including a transformer core having spaced and laterally offset pole pieces and a laterally offset rotor arranged toV rotate between said pole pieces thereby to vary the ux density between the pole pieces. Another object of this invention is the provision of a multi-stage variable transformer including a plurality of transformer units of the character :above described where- 'in each rotor is mounted on a common axis but angularly staggered with respect to the other rotors.

Still another object of this invention is the provision of Ya three-stage variable transformer of the character above described wherein the angul-ar position (phase) of each adjacent pair of transformer rotors differs by 90 degrees, whereby the summation of the resulting voltage of the transformer increases in a straight line curve over 270 degrees of rotation of the transformer rotors and then drops to zero along a straight curve during the rotation of the rotors from 270 degrees to 360 degrees.

A further object of this invention is the provision of a null-balance system wherein the rotor shaft of a multiple stage variable transformer of the character above described is driven by a 2-phase A C. servo motor; wherein the primary windings of the transformer units are in series circuit with each other and in parallelism with a reference phase winding of the servo motor; and wherein the secondary windings of the transformer unit are in series circuit with each other and arranged to oppose an input signal voltage to the control phase winding of the servo motor. Y

The invention possesses other advantageous features, some of which, with the foregoing, will be set forth at length in the following description where those forms of the invention which have been selected for illustration in the drawings accompanying and forming a part of the present specification, are outlined in full. In said drawings, one form of the invention is shown, but it is to be understood that it is notlimited to such form, since the invention as set forth in the claim may be embodied in other forms.

FIG. l is a diagrammatic illustration of a -system embodying the objects of our invention.

FIG. 2 is a vertical section taken on the line 2-2 of FIG. l.

c FIG. 3y is 'aright end elevation of the dial and pointer shown in FIG. l.

FIG. 4 is a vertical section taken on the section line 4-4 of FIG. l.

FIG. 5 is a vertical section taken on the section line 5-5 of FIG. l.

FIG. 6 is a vertical section taken on the section line 6 6 of FIG. l.

FIG. 7 is a graph of the voltage curves of the sec ondary windings of the three transformer stages shown in FIGS. l, 4, 5, and 6 resulting from the simultaneous rotation of their rotors and showing the summation of these voltages.

YICC

As illustrated in these various figures, the objects of our invention have been embodied in a system including a frame 1` provided with longitudinally spaced, coaxial bearings 2 and 3. Iournaled lin lthe bearings 2 and 3 is a transformer shaft 4, and mounted on the left end thereof as shown in FIG. l is a transmission disc 5 provided with a peripheral flange 6. Mounted on the frame 1 is a Z-phase A.C. servo motor 7 provided with a shaft 8. Ineluded in the motor 7 is areference phase coi-l or winding 9 and a control phase coil or winding 11. Fixed to the frame 1 in parallelism with the motor shaft 8 is a pin 12, and mounted thereon is Ia spacing sleeve 13. vMounted on the pin 12 is a finger 14, :a slot 14a formed in the linger 14 being provided for this purpose so that the finger is capable of rotation as well as limited translation. Mounted on the end of the pin 12 is a split washer 12a for holding the finger 14 in place.

Fixed to the free end of the finger 14 is -a pin 15. Iournaled on the pin 15 is a disc 16 arranged to be brought into fnictiona'l driving engagement with the motor shaft 8 Vand with the interior surface of the disc flange 6. Secured to and between the finger 14 and an adjacent portion of the frame 1 is -a tension spring 17 arranged to bias the disc 16 into frictional engagement with the shaft 8 and with the flange 6. Here it is to be noted that since the slot 14a permits the ngerto move longitudinally as well as to rotate, the disc 16 is free to be biased into fric- .tional engagement simultaneously with the shaft 8 and the vflange 6. This structure therefore serves as a speed reduction, friction drivebetween the motor shaft 8 and the transformer shaft 4. With an appropriate amount of tensioning force on spring 17, the torque of the motor 7 can be transmitted to the transformer shaft smoothly and without slip, up -to the motor stall.

Mounted on the frame 1 are three longitudinally spaced, laminated transformer cores 21, 22, and 23 including respectively axially offset pole pieces 21a, 2lb, 22a, 22b, and 23a, 23h. As best shown in FIG. l, the offset of each pair of these poles is in the direction of the transformer shaft 4 which for purposes of ready reference can be considered as being in a longitudinal or axial direction. From FIGS. 4,v 5, and 6 it is to be noted that the transformer core poles straddle the transformer vshaft 4.

Wound on the core 21 are primary and secondary coils 24a and 24b; wound on the core 22 are primary and secondary coils 25a and 25b; and wound on the core 23 are primary and secondary coils 26a and 26b.

Fixed to the transformer shaft 4 in cooperative relationship with the cores` 21, 22, and 23, respectively, are longitudinally offset, symmetrical, laminated rotors 27, 28, and r29. Although these rotors are of identical form, it is to be noted from FIG. ll that the rotor 28 is angularly offset degrees from the rotor 27 and that the rotor 29 is angularly offset 90 degrees from the rotor 28. As shown in FIG. l, the rotor 27 is positioned so as to completely close the air gap between its associated poles, and the rotors 28 and'29 leave the air gap between their associated shaft turns each rotor will progress to the positions previ- `ously assumed by the succeeding rotor.

Optionally associated with the shaft 4 inwardly of the bearing 3 is an instrument 31 which electively can be a recording, transmission, or control device operating in response to the rotation of the shaft.

Mounted on the frame 1 coaxially with the core shaft 4 is a calibrated dial 32 having an approximately 270 full scale, and fixed to the end of the shaft is a pointed 33 arranged to sweep over the dial.

operatively associated with the motor control phase winding is an amplifying unit 34, one side of this unit being connected with a terminal 35 through a line -36 in series circuit with the secondary coils 24b, 25b and 26b of the transformer cores. The other side of the amplifying unit is connected through a line 37 with a terminal 3-8. Although not shown, the terminals 3S and 38 are intended to be connected with some source of condition response voltage. Any change in such voltage will therefore be impressed through the amplifying unit 34 on the control winding 11,

Finally, the primary windings or coils of the transformer units are connected in series through a line 39 and connected through leads 41 and 42 with a source of alternating current, and likewise the reference phase winding or coil 9 is connected with the leads 41 and 42 through a condenser 43 and a lead 44.

Referring now to FIG.y 7, it will be seen that the rotor 27 (first stage of the transformer) in rotating through 90 degrees from its fully open position to its fully closed position, as shown in FIG. 4, results in a peak secondary output voltage 51. At this point two things happen simultaneously: the continued rotation of the rotor 27 through another 90 degrees reduces the Voltage output of the lirst stage to zero, and the rotation of the rotor 28 through 90 degrees from its fully open position to its fully closed position results in a total peak secondary voltage 52, this of course being thesummation of the secondary output voltage resulting from the rst and second stages of the transformer. At 180 degrees of rotation `0f the transformer shaft, the rotor 29 is passing through its fully open position and upon rotating through an `additional 90 degrees it reaches its fully closed position. This results in a total peak -voltage 53, the summation of the voltages resulting from the second and third stages of the transformer. When the first rotor 27 has completed 360 degrees of r0- tation of the above cycle it repeats itself.

Here it should be noted thatfor the summation of the secondary output voltages of the three stages of the transformer to approximate ,a straight line as indicated in FIG. 7, it is essential, as indicated in FIG. 4, that the arc subtended by each of the transformer core pole pieces (21a and 2lb) be 90 degrees and that the ends of each of the rotors 27, 28, and 29 be formed on a 90-degree arc.

As a result of the construction of the three-stage transformer above described, and as illustrated in FIG. 7, the rotation of the rotor shaft through 270 degrees under the influence of the servo motor 7 results in a straight line secondary output curve reaching its peak at 270 degrees, this voltage then dropping to zero through the nal 90 degrees rotation of the shaft. The secondary voltage output of each stage of the transformer of course depends upon the number of secondary turns and upon the total magnetic reluctance of the stage in question. The secondary windings are connected in series for linear voltage output in the range of to 270 degrees. Since the reluctance of each stage is almost entirely in the air gap, it is governed by the angular position of the rotor in question in relation to its pole pieces, or, in other words, by the effective area of the air gap. As previously described, the rotors of the second and third stages lag the rst stage by 90 and 180 degrees, respectively, and the secondary turns of these stages are respectively two and three times those of the rst stage. Although the shapes of the transformer rotors shown in FIGS. 1, 4, 5, and 6 will not result in the perfectly straight line voltage graphs illustrated in FIG. 7, they can be contoured so as to closely approximate these straight line graphs.

One further feature of the transformer should be noted, namely the axial offset between each core and its rotor, for it is this feature which allows each stage to go from zero to maximum output voltage over a -degree rotation, and back to zero over the ,following 90` degrees and remaining at zero over the remaining degrees of rotation. This then avoids signal repetitions at 180-degree intervals, which would preclude the use o f this device beyond 180 degrees.

By using the secondary output voltage of the transformer as a feedback to the signal voltage and in series therewith, a null detector is formed. Any error or difference between the signal voltage and the feedback voltage is arnplied by the ampliiierunit 34 and applied Vto the control phase winding 11 of the servo motor 7. The amplified error signal causes the motor to drive the shaft 4 at a proportional speed and in a direction tending to reduce the error. In view of its integrating action, the angular-position control system theoretically has a zero steady-state error.

Although for purposes of illustration, a three-stage variable transformer has been shown and described, the principles `here involved can be applied to a variable transformer having any desired number of stages. Basically, our transformer comprises a plurality of variable reluctance type transformer stages, each consisting o f a laminated core, a laminated rotor, and primary and secondary winding. Where nis the number of stages used, the linear `span of the pickoff voltage is 360n/n-i-1 degrees. Each rotor stage lags the preceding stage by S60/n+1 degrees. The vrotor and core design is such that the 'voltage output of each stage goes from zero to maximum and `back to zero over 720/n-|1 degrees.

The number of secondary turns on any core n under consideration is n times the number of secondary turns on the rst stage.

We claim;

A variable transformer comprising: a frame; a shaft journaled on said frame; a plurality of spaced, parallel transformer cores of C configuration mounted on said frame transversely of said shaft, each of said cores having axially offset poles straddling said shaft and forming an air gap thereacross; a rotor fixed to said shaft in the plane of each of said cores, each of said rotors being provided with diametrically opposed, axially oifset ends arranged in one position of said shaft to be aligned with the poles of its associated core thereby to substantially close its associated air gap, and each succeeding rotor being fixed to said shaft with a predetermined angular lag relative Ato the preceding rotor.

References Cited in the le of this patent UNITED STATES PATENTS 2,342,628 Evjen et al Feb. 29, 1944 2,451,757 Macgeorge Oct. 19, 1948 2,600,546 Kimball et al June 17, 1952 v2,630,561 Mueller Mar. 3, 1953 2,708,730 Alexander May 17, 1955 FOREIGN PATENTS 678,203 Germany July 10, 1939 

